Caroline, there are many ...

Caroline, there are many factors which affect the accuracy and display of water meter data. The type of meter technology, size, accuracy class and dynamic range are all important data points. Then comes the pulse factor - the number of times the meter rotates for each litre or cubic meter of water passing through the meter, and finally and most important in respect of your question, the read method and communication with your data display system. The International Measurement directive defines an accuracy band of +/-2% for the normal measurement range, so I don't think you need to worry about the 0.1 difference. Also, water meters are designed to under read when new and gradually over read as they speed up due to wear and age.

I assume from your question that your immediate concern is that the reading on the display system doesn't agree with the reading on the index of the meter? If you are using a magnetic pulse reader it is very unlikely that both readings will be identical because the reader can miss pulses and your display system or data logger may be externally powered and lose pulses if power or communications links fail. The only way to ensure identical readings is to use a smart meter with a direct electronic reader such as M-Bus.